- It's too early to free the SSL object in 'vio_ssl_close'. There
   might still be a thread using or reading from it on platforms
   where we need to close the active connection/socket in order
   to break the read.  
 - Add new function 'vio_ssl_delete' and install it as the viodelete
   function for SSL connections.


vio/vio.c:
  Install 'vio_ssl_delete' as viodelete function for SSL connections
  Cleanup 'vio_delete'
vio/vio_priv.h:
  Add declaration of vio_ssl_delete
vio/viossl.c:
  Add new function 'vio_ssl_delete' that takes care of freeing the memory
  allocated by the SSL connection
  Move the code to free the SSL object from vio_ssl_close